This invention relates generally to blow molded wide-mouth polyethylene terephythalate (PET) plastic containers, and more particularly to such containers having a threaded neck.
Wide mouth PET bottles having threaded necks typically have neck finishes larger than 48 mm in diameter, and the majority of those bottles are produced on single stage injection mold equipment. This equipment is well suited for low volume applications primarily because the slower injection process is the determining factor in cycle time. For high volume applications two-stage PET equipment has been developed to make preforms having the desired finished threaded neck configuration in a separate injection molding machine and then reheating and blowing the preforms in another blowing machine. However, in this arrangement the blowing machine can out-produce the injection machine and preform inventories must be carefully monitored to keep an adequate supply for the blowing machine. This imbalance is compounded when two-stage equipment is used in wide mouth applications. This is primarily due to the size of the preform/neck finish and the physical size of the injection mold.
To overcome those problems in producing wide mouth threaded neck bottles in large volumes for particular use in cold fill applications, we decided to try to use narrow neck preforms to blow the neck finish using the process generally illustrated in U.S. Pat. Nos. 4,496,064, 4,894,268 and 6,228,317. In such a process a standard narrow neck preform is blow molded to form an intermediate article which includes a lower portion in the configuration of the desired bottle with threaded neck and an upper accommodation or dome portion. The dome portion is subsequently removed to provide the finished bottle. However, because of the strain hardening characteristics of PET, it was difficult to get the smaller diameter preform material to blow out and form acceptable, useable neck finish threads on cold fillable containers for a viscous product such as mayonnaise.
Accordingly, the wide mouth PET container and its method of manufacture described below were developed to overcome the those problems.